Process for the treatment of nodular cast iron

ABSTRACT

A process for the treatment of molten iron to produce castings having a graphite nodular structure in which the molten cast iron is first treated with a nodulating alloy containing magnesium and boron and then with an inoculating alloy containing silicon and barium.

United States Patent Percheron et al. [451 May 9, 1972 54] PROCESS FOR THE TREATMENT OF [56] References Cited NODULAR CAST IRON UNITED STATES PATENTS [72] Inventors: Jean-Claude G. Percheron; Louis Septier, v

both of Chedde, France 2,450,395 9/1948 Eckman et a1 ..75/123 B X 2,676,097 4/1954 Strauss ....75/1 30 A X [73] Assignee: Compagnie Pechlney, Pans, Franceby said 2,778,732 1/1957 Aebefly ct a| "75H 30 R Pmhew" 2,816,829 12 1957 Bogart ..75/l30 A x [22] Filed: Sept. 30, 1969 Primary EraminerL. Dewayne Rutledge [2 H App! 862343 Assistant E.\'aminer.l. E. Legru An0rneyMcDougall, Hersh, Scott & Ladd [30] Foreign Application Priority Data Oct. 2. 1968 France ..168451 [57} ABSTRACT A process for the treatment of molten iron to produce castings [52] U.S. Cl. ..75/130 R, 75/123 CB, 75/130 A, having a graphite nodular structure in which the molten cast 75/130 75/134 5 iron is first treated with a nodulating alloy containing magnesi- [51] Int. Cl ..C22c 23/00, C22c 37/04 um d boron d h with an inoculating alloy containing of Search B, L, CB, B, ilicon and barium 75/130 A, 130 AB, 130 R, 130 C, 130 BB 4 Claims, 4 Drawing Figures PROCESS FOR THE TREATMENT OF NODULAR CAST IRON This invention relates to the production of nodular iron and more particularly to a process for the treatment of molten iron in the production of castings in which the graphitic components provide a nodular structure.

It is well known to subject molten iron to nodulating treatment and then to an inoculating treatment shortly before casting to obtain castings having a nodular graphitic structure. Such castings generally undergo a thermal treatment which has the effect of dissolving the carbides and transforming the iron matrix into ferrite or pearlite, or combinations thereof, depending somewhat upon the desired mechanical properties.

Such nodulating treatment consists of introducing pure magnesium or an alloy of magnesium, such as an Fe-Si-Mg alloy, into the molten iron. The inoculating treatment consists of the addition of silicon or an alloy containing silicon, such as an Fe-Si alloy, to the molten iron. The efficiency of the nodulating or inoculating metal or alloy can be improved by the addition of elements. For example, calcium, cesium, yttrium and rare earths are known to improve nodulation while barium is known to improve the effect of the inoculating alloys.

It is an object of this invention to provide a new and improved method for producing nodular iron.

It has been found, in accordance with the practice of this invention, that the combination of a nodulating alloy containing boron in addition to magnesium and an inoculating alloy containing barium in addition to silicon gives results that differ materially by comparison with the use of boron or barium alone in one of the alloys. It has been found that iron castings treated by the combination of boron in the nodulating alloy and barium in the inoculating alloy yields castings which, in the as cast state, are remarkably free of carbides. The described inoculating-nodulating combination of barium and boron has a marked ferritization effect on the iron matrix and, for a given composition of iron, it is possible to obtain a more or less ferritized matrix, depending upon the proportions of the nodulating and inoculating alloy selected.

The absence of carbides plus the possibility to determine the structure of the matrix makes it possible drastically to reduce the length of the final heat treatment. Aside from the reduction in cost, it is most desirable to be able to shorten final heat treatment because otherwise the heat treatment modifies or alters the surface aspects of the castings.

In the practice of the invention, the nodulating alloy is selected to contain an amount of boron such that the ratio of weight percent magnesium and the weight percent of boron meets the following conditions:

10 Mg %lB l and preferably l Mg %IB 30 and when, on the other hand, the inoculating alloy contains barium in the ratio of weight percent silicon and weight percent of barium to meet the following conditions:

3 Si %lBa and preferably 4 Si%/Ba% l2 The following examples are given by way of illustration and not by way of limitation. Examples 1, 2 and 3 do not represent the practice of this invention. Example 1 illustrates the prior art and Examples 2 and 3 illustrate the use of boron alone or barium alone. Examples 4, 5 and 6 represent the practice of this invention wherein the nodulating alloy contains boron and the inoculating alloy contains barium. Example 7 illustrates the non-equivalency between barium and calcium insofar as the practice of this invention is concerned.

The FIGS. 1, 2, 3 and 4 of the accompanying drawing are photomicrographs of the cast metals of Examples 1, 2, 3 and 4.

EXAMPLE I In a ladle containing 75 kg of molten iron at 1,510 C, 2.250

kg of Fe-Si-Mg nodulating alloy (Mg 9. 1 percent) are added with a plunger. As soon as the plunger isbrought up, 0.375 kg of Fe-Si inoculating alloy (Si 75 percent) are added.

The metal is cast after 9 minutes.

EXAMPLE 2 This example is the same as Example 1 except that 2.250 kg of Fe-Si-Mg-B (Mg 9.1 percent, B 0.48 percent) and 0.375 kg of Fe-Si (Si 75 percent) are used.

EXAMPLE 3 The example is the same as Example 1 except that 2.250 kg of Fe-Si-Mg (Mg 9.25 percent) and 0.420 kg of Fe-Si-Ba (Si 59.5 percent, Ba= 9.8 percent) are used.

EXAMPLE 4 The process is the same as in Example I but, in accordance with the practice of the invention, use is made of 2.250 kg of Fe-Si-Mg-B (Mg 9.1 percent, B 0.48 percent) and 0.420 kg of Fe-Si-Ba (Si 59.5 percent, Ba 9.8 percent).

The composition of the iron after casting and the properties of thin castings before heat treatment are set forth in the following Table I. The accompanying micrographic reproductions clearly show that only the process embodying the practice of this invention yields castings which are free of carbides, an important percentage of ferrite in the matrix and high values for elongation at rupture.

Similar results could also be obtained by the process described in Examples 1, 2 or 3 but a lengthy heat treatment would be required to dissolve the carbides and to modify the carbon distribution.

Table i and the micrographs also show that the process of the invention gives a much higher magnesium efficiency (eval- TABLE I Example 4, Example 1, Example 2, Example 3, according no B, with B, no B, to the no Ba no Be With Ba invention Chemical composition after a nodulating and inoculating treatment, percent:

C 3. 60 3. 58 3. 3.55. Si 2. 00 2. 65 2. 54 2.70. Mn 0.05 0. 06 0.05 0.08. P v 0. 023 0.021 0.025 0. 026. S 0. 007 0. 007 0. 000 0.010. Mg 0. 040 0. 046 0. 038 0.048. Castings characteristics before heat treatment:

Ferrite in the matrix Ferrite-pearlite Mostly ferrite (90%) Number of nodules/mm 80110 :1:10 :l=15 105110. Presence of enbrides Yes Yes Few Very few. R, ultimate strength, lrg/mm. 43.4 44. 2 48 51.8. Elongation, percent 6.7 9.4 13.4 18.0. E, elastic limit kgjmrni 25. 6 26. 3 28.2.

'Stnndnrd test pieces.

uated by the residual Mg content), increases the number of graphite nodules and regulates their size.

EXAMPLE 5 C .6 Si P S Mg 0.052

The mechanical properties, determined on the as cast test pieces are:

ultimate strength 50 kg/mm elongation at rupture 17 percent EXAMPLE 6 One ton (1,000 kg) of molten iron at l,480 C is treated by the "Sandwich procedure" by 14 kg of Fe-Si-Mg-B alloy present in the following amounts:

Si 45. Mg 8.1 a 0.45 Ca 0.07

0.2 kg of silico mischmetal is then introduced with a plunger. The melt is then inoculated with 12 kg of Fe-Si-Ba (Si 60.1 percent, Ba= 9.4 percent).

The castings obtained have a perfectly nodular graphite structure and a highly ferritic matrix. The mechanical properties in the as cast condition are:

elastic limit 38 kgJmm.

ultimate strength 52.3 kgJmm.

elongation at rupture 13.2%

EXAMPLE 7 150 kg of molten iron are divided into two equal portions A Si Mg 7.95%

The following are introduced with a plunger: v

In fraction A: 0.420 kg of Fe-Si-Ba alloy (Si 61 percent, Ba 9.6 percent). This fraction, which represents the practice of this invention, gives castings which are as good as those of Example 4.

1n fraction B: 0.420 kg of the alloy Fe-Si-Ca (Si 62.4 percent, Ca 10.3 percent). As with fraction A, the castings obtained have a good surface appearance but present a slight piping tendency. As Table 11 clearly shows, the castings made with fraction B contain more carbides and less ferrite.

TABLE II Percent Fraction A, according to the invention Fraction l3 Composition alter nodulating and inoculating trcatnmnt:

,H, 3.07 3.01 hi 2. 67 1.75 M n 0. l 0. l l 0. 0'1 0. 02 S 0. 000 0. 008 M 0.048 0.044 Properties lmlorv lu-ul. trmitnw|1l.:

Ferrite in the matrix J0 75 1 on. 5

lrvsonuv of carbides 1. A process for obtaining a nodular graphite structure in cast irons wherein a nodulating alloy containing Mg and boron in the ratio of weight percentages within the range of 10 to and an inoculating alloy containing silicon and barium in the ratio of weight percentages within the range of 3 to 60 are successively introduced into molten cast iron.

2. A process as clauned in claim 1 in which the nodulating alloy contains magnesium and boron in the ratio of weight percentages within the range of 15 to 30.

3. A process as claimed in claim 1 in which the inoculating alloy contains silicon and barium in the ratio of weight percentages within the range of 4 to 12.

4. A process as claimed in claim 1 in which the nodulating alloy contains magnesium and boron in the ratio in weight percentage within the range of 15 to 30 and in which the inoculating alloy contains silicon and barium in the ratio of weight percentage within the range of 4 to 12.

* l i =l l 

2. A process as claimed in claim 1 in which the nodulating alloy contains magnesium and boron in the ratio of weight percentages within the range of 15 to
 30. 3. A process as claimed in claim 1 in which the inoculating alloy contains silicon and barium in the ratio of weight percentages within the range of 4 to
 12. 4. A process as claimed in claim 1 in which the nodulating alloy contains magnesium and boron in the ratio in weight percentage within the range of 15 to 30 and in which the inoculating alloy contains silicon and barium in the ratio of weight percentage within the range of 4 to
 12. 